1. Field of the Invention
The present invention relates to a tape carrier package which is attached to the periphery of a liquid crystal panel of a liquid crystal display device and accommodates a semiconductor chip for driving the liquid crystal panel on a tape carrier, and a liquid crystal display device provided with tape carrier packages.
2. Description of the Related Art
Conventional liquid crystal display devices as shown in FIG. 10 have been known. This liquid crystal display device 150 is mainly composed of a liquid crystal panel 100, a plurality of tape carrier packages (TCPs) 117, and a common printed wiring board 118. The liquid crystal panel 100 is mainly composed of an upper glass substrate 110, a lower glass substrate 111, and a liquid crystal layer (not shown) interposed therebetween. Reference numeral 122 denotes to a flexible substrate.
In this liquid crystal display device, as shown in FIG. 13, the semiconductor chips 104 for driving the liquid crystal are mounted onto the liquid crystal panel 100 as follows: A tape carrier with semiconductor chips 104 placed thereon is cut to a predetermined size to obtain TCPs 117; each TCP 117 is supplied onto the liquid crystal panel 100; and a conducive pattern portion (e.g., outer leads) of each TCP 117 and electrodes on the lower glass substrate 111 of the liquid crystal panel 100 are crimped onto each other by heating with an anisotropic conductive film 140 interposed therebetween, whereby each TCP 117 is mounted onto the liquid crystal panel 100.
As shown in FIG. 13, outer leads (not shown) of the TCPs 117 are connected to wiring (not shown) of the printed wiring board 118. A signal for driving the liquid crystal is supplied to each semiconductor chip 104 through each TCP 117 from the printed wiring board 118. The printed wiring board 118 also has a region 118a for accommodating components such as a chip capacitor which cannot be incorporated into the circuit of each semiconductor chip 104.
FIG. 11 is a cross-sectional view of another liquid crystal display device 160 with a TCP 117' attached to the periphery of a liquid crystal panel 100. The TCP 117' is attached to the liquid crystal panel 100 as follows: an output terminal 117a of the TCP 117' for driving the liquid crystal is connected to the liquid crystal panel 100 via an anisotropic conductive film 140; thereafter, an input signal terminal 117b of the TCP 117' is connected to a printed wiring board 118 by soldering or via an anisotropic conductive film 140'; and the TCP 117' is bent along the contour of a module, whereby the attachment of the TCP 117' to the liquid crystal panel 100 is complete. In FIG. 11, reference numeral 119 denotes a backlight unit; 120 denotes a polarizing plate; and 116 denotes a bezel.
It is also known that a semiconductor chip is attached to a liquid crystal panel by a Chip-On-Glass (COG) method. According to the COG method, as shown in FIG. 12, a semiconductor chip 104 having metal bumps 104a is directly connected to wiring (not shown) on a lower glass substrate 111 by face down bonding. Regarding the COG method, the following two processes are known.
Firstly, a semiconductor chip having solder bumps is directly attached to a glass substrate of a liquid crystal panel, and then, a gap between the semiconductor chip and the glass substrate is filled with a resin (Japanese Laid-Open Patent Publication No. 4-105331). Secondly, a semiconductor chip having gold bumps is connected to wiring on a glass substrate of a liquid crystal panel via an anisotropic conductive film 121 (Japanese Laid-Open Patent Publication Nos. 4-76929, 4-71246, and 4-317347). In the case of the second process, a gap between the semiconductor chip and the glass substrate is filled with a resin (binder) of the anisotropic conductive film. According to the second process, repairs are easily conducted, and it is not required to fill a resin in the gap between the semiconductor chip and the glass substrate; therefore, this process has been mainly used.
In recent years, there is a tendency to secure a larger display area with the same module size by decreasing the width of the portion of a liquid crystal display device that extends off a glass substrate. Furthermore, there is a great demand for a reduction in costs for liquid crystal panels in light of the generally, higher production costs compared with those of CRTs (Cathode Ray Tube).
Under such circumstances, in order to decrease the width of a TCP which extends off a glass substrate, the following two methods using TCPs have been proposed: (1) A slim-type TCP 117 with a narrow semiconductor chip formed thereon is used as shown in FIG. 13 (Japanese Design Patent Application No. 2-40145); and (2) as described with reference to FIG. 11, a portion of a TCP 117' which extends off a glass substrate is bent (Japanese Laid-Open Patent Publication No. 2-132418).
According to the method as shown in FIG. 13, a material used for a TCP itself is also reduced, which contributes to a reduction in costs. However, it is necessary to decrease the width of a portion of a TCP which extends off a glass substrate. When the width of the printed wiring board is decreased without changing the wiring density, it is necessary to increase the number of layers of the printed wiring board. This results in an increase in costs. In addition, since the width of a connected portion of the printed wiring board and the TCP is very small, it is difficult to mount the TCP onto the printed wiring board. This may influence the yield and reliability of a device to be obtained. These problems become serious in circumstances where liquid crystal panels are increasing in size.
As shown in FIG. 13, even when the above-mentioned slim-type TCP is used, a portion with a width of about 5 mm necessarily extends off the glass substrate. FIG. 10 is a schematic plan view (the bezel 116 is omitted) of a liquid crystal panel constructed as illustrated in FIG. 13.
In the case where the bent TCP 117' is used as shown in FIG. 11, the printed wiring board 118 may be provided either on the upper surface or on the lower surface of the lower glass substrate 111. In the case where the printed wiring board 118 is provided on the lower surface of the lower glass substrate 111, the wiring of the liquid crystal panel 100 can be connected to the printed wiring board 118 can be prevented from extending off the liquid crystal panel 100. Accordingly, the problem associated with the large size of devices can be solved to some degree. In the case as shown in FIG. 11, the width of a portion of the TCP which extends off the glass substrate is only 2 mm (which is much smaller than that in the case as shown in FIG. 13).
However, in the case of using the bent TCP 117', there are the following problems: it is required to prescribe the length of the TCP 117' to be larger by the bent portion thereof, so that costs for a tape carrier portion of the TCP 117' cannot be minimized; it is easier to connect the printed wiring board 118 to the TCP 117', compared with the case where the above-mentioned slim-type TCP 117 is used, however, it is required to bend the TCP 117' to a predetermined shape after the TCP 117' is connected to the printed wiring board 118 so that the TCP 117' is fixed to the printed wiring board 118; and the thickness of a liquid crystal module becomes larger by the total thickness of the printed wiring board 118 and the TCP 117' (i.e., about 2.5 mm to 3 mm), compared with the case where the slim-type TCP 117 as shown in FIG. 13 is used.
According to the COG method, a semiconductor chip is directly mounted onto a glass substrate, so that the costs for packaging are less, compared with the case where a TCP is used. Furthermore, when an input signal is adapted to be supplied to a semiconductor chip via wiring on a glass substrate, a printed wiring board is not required. This results in a decrease in costs. Still furthermore, according to the COG method, a semiconductor chip is merely mounted onto a glass substrate, so that the costs for mounting can be reduced.
However, the above-mentioned advantages cannot be obtained from currently used large liquid crystal panels with a 10-inch or more diagonal screen for the following reason: the sheet resistance of a material for wiring on a glass substrate is high; therefore, in the case where an input signal is supplied to a semiconductor chip via wiring on the glass substrate, the wiring resistance cannot be minimized; and as a result, voltage drops in the wiring, which makes it impossible to transmit a normal signal to a semiconductor chip. In relatively small liquid crystal panels with about a 3- to 6-inch diagonal screen, wiring length is small, so that the sheet resistance of a material for wiring is negligible. Accordingly, the above-mentioned advantages can be obtained only from such relatively small liquid crystal panels.
However, when the above-mentioned structure is applied to small liquid crystal panels using the COG method, there are the following problems: since it is required to prescribe the width of wiring on a glass substrate to be large, the area of the glass substrate for mounting semiconductor chips is required to be made larger, compared with the case where TCPs are used; this requires the size of the glass substrate to be increased. In this case, the number of liquid crystal panels obtained from mother glass decreases. Thus, even in the case where the COG method is used for small liquid crystal panels, cost is not likely to decrease as far as an entire module is concerned.
In order to solve the problem associated with the enlargement of an area of a glass substrate for mounting semiconductor chips, as shown in FIG. 12, it is possible to adopt a method for directly connecting a flexible substrate 122 to the wiring on a glass substrate in the vicinity of a portion for mounting each semiconductor chip 104 and transmitting an input signal from the flexible substrate 122. (Japanese Laid-Open Utility Model Publication No. 4-77134). According to this method, a printed wiring board is not required, however, the flexible substrate 122 is used. Therefore, the advantages in terms of lower production costs and fewer steps cannot be obtained.
Furthermore, according to the COG method, bare chips are supplied onto a glass substrate. The bare chips are generally tested in a wafer state, and they are not tested after being divided into individual chips by dicing. Thus, it is difficult to judge whether or not a particular semiconductor chip to be mounted onto a glass substrate is satisfactory. That is, a semiconductor chip to be mounted is not a "known good die". Because of this, in the case of a large liquid crystal panel in which a number of semiconductor chips are mounted, there are more chances of failure and repairs, resulting in an increase in costs.